U.S. patent application number 12/099755 was filed with the patent office on 2008-10-16 for apparatus and method for uplink bandwidth request in broadband wireless access system.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO. LTD.. Invention is credited to Han-Seok KIM, Jae-Young KIM, Eun-Chan PARK.
Application Number | 20080253325 12/099755 |
Document ID | / |
Family ID | 39485150 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080253325 |
Kind Code |
A1 |
PARK; Eun-Chan ; et
al. |
October 16, 2008 |
APPARATUS AND METHOD FOR UPLINK BANDWIDTH REQUEST IN BROADBAND
WIRELESS ACCESS SYSTEM
Abstract
An UpLink (UL) bandwidth requesting apparatus and method in a
broadband wireless access system are provided. The apparatus
includes a queue length controller for determining an amount of
bandwidth-request using a difference between a current queue length
and a target length and a determiner for the final amount of
bandwidth-request using a change rate of queue length for sending
information of the calculated bandwidth-request amount to a
bandwidth allocating apparatus. By rapidly and accurately
predicting the bandwidth-request and reducing the request delay,
Quality of Service (QoS) can be guaranteed using a minimum
bandwidth.
Inventors: |
PARK; Eun-Chan;
(Seongnam-si, KR) ; KIM; Han-Seok; (Seoul, KR)
; KIM; Jae-Young; (Yongin-si, KR) |
Correspondence
Address: |
Jefferson IP Law, LLP
1730 M Street, NW, Suite 807
Washington
DC
20036
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.
LTD.
Suwon-si
KR
|
Family ID: |
39485150 |
Appl. No.: |
12/099755 |
Filed: |
April 8, 2008 |
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 72/1252 20130101;
H04W 72/1284 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2007 |
KR |
2007-0036253 |
Claims
1. An UpLink (UL) bandwidth requesting apparatus in a wireless
access system, comprising: a queue length controller for
determining an amount of bandwidth-request using a difference
between a current queue length and a target queue length; and a
determiner for the final amount of bandwidth-request for sending
information of the determined bandwidth-request amount to a
bandwidth allocating apparatus.
2. The UL bandwidth requesting apparatus of claim 1, further
comprising: a detector of queue length change for estimating a
change rate of queue length; and a rate controller of queue length
for determining a amount of bandwidth-request in proportion to the
estimated change rate of queue length, wherein the determiner for
the final amount of bandwidth-request determines an amount of a
bandwidth-request by adding the two bandwidth-request amounts and
sends information of the determined final bandwidth-request amount
to the bandwidth allocating apparatus.
3. The UL bandwidth requesting apparatus of claim 2, wherein The
detector of queue length change estimates the change rate of queue
length using a difference between a packet arrival rate of the
queue and a service rate.
4. The UL bandwidth requesting apparatus of claim 1, wherein the
bandwidth-request amount comprises at least one of an increase and
a decrease from an amount of a previous bandwidth-request.
5. The UL bandwidth requesting apparatus of claim 1, wherein the
queue length controller sets a value greater than the target length
by a certain value as an upper threshold, sets a value smaller than
the target length by a certain value as a lower threshold,
determines an additional bandwidth-request as a first preset size
when the current queue length exceeds the upper threshold, and
determines a reduced bandwidth-request as a second preset size when
the current queue length falls below the lower threshold.
6. The UL bandwidth requesting apparatus of claim 5, wherein the
queue length controller determines the bandwidth-request as zero
when the current queue length lies between the upper threshold and
the lower threshold.
7. The UL bandwidth requesting apparatus of claim 1, wherein the
queue length controller determines the bandwidth-request in
proportion to an error between the current queue length and the
target length.
8. The UL bandwidth requesting apparatus of claim 1, wherein, to
determine the bandwidth-request in proportion to the error between
the current queue length and the target length, the queue length
controller sets a value greater than the target length by a certain
value as an upper threshold, sets a value smaller than a target
length by a certain value as a lower threshold, and determines the
bandwidth-request as zero when the current queue length lies
between the upper threshold and the lower threshold.
9. The UL bandwidth requesting apparatus of claim 1, wherein the
information of the determined bandwidth-request amount is
transmitted by piggybacking on UL packets.
10. An UpLink (UL) bandwidth requesting method in a wireless access
system, comprising: determining an amount of bandwidth-request
using a difference between a current queue length and a target
queue length; and sending information of the determined
bandwidth-request amount to a bandwidth allocating apparatus.
11. The UL bandwidth requesting method of claim 10, further
comprising: estimating a change rate of queue length; determining
an amount of bandwidth-request in proportion to the estimated
change rate of queue length; and determining an amount of a final
additional bandwidth-request by adding the two bandwidth-request
amounts, wherein the sending of the information to the bandwidth
allocating apparatus comprises sending information of the
determined final bandwidth-request amount to the bandwidth
allocating apparatus.
12. The UL bandwidth requesting method of claim 11, wherein the
estimating of the change rate of queue length comprises using a
difference between a packet arrival rate of the queue and a service
rate.
13. The UL bandwidth requesting method of claim 10, wherein the
determining of the amount of bandwidth-request comprises at least
one of increasing and decreasing an amount of a previous
bandwidth-request.
14. The UL bandwidth requesting method of claim 10, wherein the
determining of the bandwidth-request amount comprises: setting a
value greater than the target length by a certain value as an upper
threshold and setting a value smaller than the target length by a
certain value as a lower threshold; and determining an additional
bandwidth-request as a first preset size when the current queue
length exceeds the upper threshold and determining a reduced
bandwidth-request as a second preset size when the current queue
length falls below the lower threshold.
15. The UL bandwidth requesting method of claim 14, wherein the
determining of the bandwidth-request amount comprises: determining
the bandwidth-request as zero when the current queue length lies
between the upper threshold and the lower threshold.
16. The UL bandwidth requesting method of claim 10, wherein the
determining of the bandwidth-request amount comprises determining
the bandwidth-request in proportion to an error between the current
queue length and the target length.
17. The UL bandwidth requesting method of claim 10, wherein the
determining of the bandwidth-request in proportion to the error
between the current queue length and the target length comprises
setting a value greater than the target length by a certain value
as an upper threshold, setting a value smaller than a target length
by a certain value as a lower threshold, and determining the
bandwidth-request as zero when the current queue length lies
between the upper threshold and the lower threshold.
18. The UL bandwidth requesting method of claim 10, wherein the
sending of the information of the determined bandwidth-request
comprises transmitting the information by piggybacking on UL
packets.
Description
PRIORITY
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(a) of a Korean patent application filed in the Korean
Intellectual Property Office on Apr. 13, 2007 and assigned Serial
No. 2007-36253, the entire disclosure of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to an apparatus and
a method for an UpLink (UL) bandwidth request in a broadband
wireless access system. More particularly, the present invention
relates to an apparatus and a method for ensuring Quality of
Service (QoS), assuring delay requirement and efficiently
requesting a desired UL bandwidth using a fast and accurate
estimation of the desired bandwidth in consideration of both a
queue length and a change rate of queue length.
[0004] 2. Description of the Related Art
[0005] The Institute of Electrical and Electronics Engineers (IEEE)
802.16e standard classifies services based on service requirements
such as transmission delay time, jitter, and minimum required data
rate, and defines several schemes for scheduling and UpLink (UL)
bandwidth request/allocation to meet the Quality of Service (QoS)
requirements for different classes of service.
[0006] An example of a scheduling scheme is the Unsolicited Grant
Service (UGS). According to the UGS scheme, a base station
allocates a fixed-sized bandwidth to a subscriber station on a
periodic basis without a request from the subscriber station. The
UGS scheme is typically used for applications such as Voice over
Internet Protocol (VoIP)
[0007] An example of a bandwidth requesting and scheduling scheme
is the real-time Polling Service (rtPS). In the rtPS scheme, a base
station periodically polls a subscriber station by granting a
bandwidth-request opportunity. The subscriber station responds by
requesting a bandwidth from the base station at an amount to
support the desired service of the subscriber station. And then the
base station assigns the bandwidth to the subscriber station. The
rtPS scheme is typically used as a requesting and scheduling scheme
for an application that generates variable-sized packets on a
periodic basis, such as a video streaming application.
[0008] An extended rtPS (ertPS), which is newly defined by the IEEE
802.16e, is a bandwidth request/allocation scheme that combines the
advantages of the UGS and the rtPS. In the ertPS scheme, the base
station assigns a fixed-sized bandwidth to the subscriber station
at periodic intervals without a request from the subscriber
station. The base station can increase or decrease the amount of
the allocated bandwidth according to a request received from the
subscriber station. Thus, the ertPS is suitable for real-time
applications generating a variable data rate, for example, VoIP
service with silence suppression or multimedia service. Compared to
the UGS scheme, the ertPS scheme provides more efficient bandwidth
utilization. And compared to the rtPS scheme, the ertPS scheme
provides the bandwidth request in a piggyback manner without
polling for the bandwidth request and thus reduces transmission
delay.
[0009] In addition to the bandwidth request/allocation schemes for
the non-real-time application, a non-real-time Polling Service
(nrtPS) requests the bandwidth through the polling to ensure the
minimum required data rate and a Best Effort (BE) does not have any
service requirements.
[0010] As discussed above, the IEEE 802.16e standard defines the
ertPS scheduling mechanism for efficient UL bandwidth
request/allocation for variable-rate real-time traffic. However,
the standard does not define a specific algorithm for
bandwidth-request adaptation.
SUMMARY OF THE INVENTION
[0011] An aspect of the present invention is to address at least
the above mentioned problems and/or disadvantages and to provide at
least the advantages described below. Accordingly, an aspect of the
present invention is to provide an apparatus and a method for an
UpLink (UL) bandwidth request in a broadband wireless access
system.
[0012] Another aspect of the present invention is to provide an
apparatus and a method for satisfying Quality of Service (QoS)
while minimizing delay violation probability and efficiently
requesting a UL bandwidth in a broadband wireless access
system.
[0013] Yet another aspect of the present invention is to provide an
apparatus and a method for determining a proper amount of
bandwidth-request using a queue length and a change rate of queue
length in an extended real-time Polling Service (ertPS) scheme of a
broadband wireless access system.
[0014] In accordance with an aspect of the present invention, a UL
bandwidth requesting apparatus in a broadband wireless access
system is provided. The apparatus includes a queue length
controller for calculating an amount of bandwidth-request using a
difference between a current queue length and a target queue
length, and a determiner for the final amount of bandwidth-request
a final amount of bandwidth-request based on a change rate of queue
length.
[0015] In accordance with another aspect of the present invention,
a UL bandwidth requesting method in a broadband wireless access
system is provided. The method includes calculating an amount of
bandwidth-request using a difference between a current queue length
and a target queue length and sending information of the calculated
bandwidth-request amount to a bandwidth allocating apparatus.
[0016] Other aspects, advantages, and salient features of the
invention will become apparent to those skilled in the art from the
following detailed description, which, taken in conjunction with
the annexed drawings, discloses exemplary embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other aspects, features and advantages of
certain exemplary embodiments the present invention will become
more apparent from the following description taken in conjunction
with the accompanying drawings, in which:
[0018] FIG. 1 is a block diagram illustrating an apparatus for
requesting an UpLink (UL) bandwidth and an apparatus for allocating
a UL bandwidth in a broadband wireless access system according to
an exemplary embodiment of the present invention;
[0019] FIG. 2 is a flowchart illustrating a method of requesting a
UL bandwidth according to an exemplary embodiment of the present
invention;
[0020] FIG. 3 is a flowchart illustrating a method of allocating a
UL bandwidth according to an exemplary embodiment of the present
invention;
[0021] FIGS. 4A to 4C are flowcharts illustrating various methods
of calculating an amount of bandwidth-request according to
exemplary embodiments of the present invention;
[0022] FIG. 5 is a graph for comparing a queue length variation
between a conventional method and an exemplary algorithm of the
present invention; and
[0023] FIG. 6 is a graph for comparing a packet arrival rate and a
queue service rate according to an exemplary algorithm of the
present invention.
[0024] Throughout the drawings, it should be noted that like
reference numbers are used to depict the same or similar elements,
features and structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0025] The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
exemplary embodiments of the present invention as defined by the
claims and their equivalents. It includes various specific details
to assist in that understanding but these are to be regarded as
merely exemplary. Accordingly, those of ordinary skill in the art
will recognize that various changes and modifications of the
embodiments described herein can be made without departing from the
scope and spirit of the invention. Also, descriptions of well-known
functions and constructions are omitted for clarity and
conciseness.
[0026] Exemplary embodiments of the present invention provide an
apparatus and a method for requesting an UpLink (UL) bandwidth in a
broadband wireless access system. In the following examples, a
bandwidth requesting apparatus is implemented in a subscriber
station and a bandwidth allocating apparatus is implemented in a
base station.
[0027] FIG. 1 is a block diagram illustrating an apparatus for
requesting a UL bandwidth and an apparatus for allocating a UL
bandwidth in a broadband wireless access system according to an
exemplary embodiment of the present invention.
[0028] The bandwidth requesting apparatus 100 of FIG. 1 includes a
queue 102, a queue length controller 104, a determiner for the
final amount of bandwidth-request 106, a detector of queue length
change 108, and a rate controller of queue length 110. The
bandwidth allocating apparatus 120 includes a UL scheduler 122.
[0029] The queue 102 of the bandwidth requesting apparatus 100
queues incoming UL data. Because data transmission is limited by
the bandwidth assigned to the subscriber station, the packets in
the queue 102 are served only at the rate of the bandwidth assigned
by the bandwidth allocating apparatus 120. The queue 102 outputs
the queued data to a transmitter (not shown).
[0030] The queue length controller 104 monitors the current length
of the queue 102 and determines an amount y.sub.q(t) of a
bandwidth-request using a difference between a desired target or
reference length q.sub.ref of the queue 102 and the observed actual
length q(t), i.e., e.sub.q(t)=q(t)-q.sub.ref, and outputs the
determined amount of bandwidth-request to the determiner for the
final amount of bandwidth-request 106. Herein, the amount of
bandwidth-request indicates an increase or a decrease from the
amount of a previous bandwidth-request. Otherwise, the amount of
bandwidth-request may correspond to the whole amount of bandwidth
required supporting the desired QoS.
[0031] The detector of queue length change 108 estimates a change
rate e.sub.r(t)=a(t)-s(t) of the queue length 102. That is, the
detector of queue length change 108 determines a difference between
the packet arrival rate a(t) and the service rate s(t) and outputs
the estimated change rate of queue length to the rate controller of
queue length 110.
[0032] The rate controller of queue length 110 computes the amount
of bandwidth-request in proportion to the change rate of queue
length e.sub.r(t), and outputs the computed amount of
bandwidth-request to the determiner for the final amount of
bandwidth-request 106.
[0033] The determiner for the final amount of bandwidth-request 106
determines the amount of a final additional bandwidth-request by
adding the amounts of the bandwidth-request provided from the queue
length controller 104 and the rate controller of queue length 110,
and sends information of the determined final bandwidth-request
amount to the bandwidth allocating apparatus 120. Herein, the
information of the final bandwidth-request amount can be
transmitted by piggybacking on UL packets.
[0034] The UL scheduler 122 of the bandwidth allocating apparatus
120 receives the information of the final bandwidth-request amount
from the bandwidth requesting apparatus 100, and assigns the
bandwidth to the bandwidth requesting apparatus 100 using the
received information through UL scheduling. Next, a data receiver
(not shown) receives UL data using the assigned bandwidth.
[0035] FIG. 2 is a flowchart illustrating a method of requesting a
UL bandwidth according to an exemplary embodiment of the present
invention.
[0036] In step 201, the bandwidth requesting apparatus observes the
current queue length q(t) and estimates the change rate e.sub.r(t)
of the queue length by determining the difference between the
packet arrival rate a(t) and the service rate s(t) of the queue. In
step 203, the bandwidth requesting apparatus determines the amount
y.sub.q(t) of the bandwidth-request using the current queue length
q(t) and the reference length q.sub.ref. Herein, the
bandwidth-request amount indicates an increase or a decrease of the
amount from the previous bandwidth-request.
[0037] The bandwidth-request amount can be computed in various ways
using the difference between the current queue length and the
reference length. For example, as shown in FIG. 4A, a value greater
than the reference length by a certain size is set to an upper
threshold q.sub.th.sup.max and a value smaller than the reference
length by a certain size is set to a lower threshold
q.sub.th.sup.max. When the current queue length is observed to
exceed the upper threshold, the bandwidth requesting apparatus can
request additional bandwidth of quantity .DELTA..sub.+. Here,
.DELTA..sub.+ is a predefined design parameter. Similarly, when the
current queue length falls below the lower threshold, the bandwidth
requesting apparatus can request to decrease the bandwidth by
.DELTA.- with respect to the previous bandwidth-request amount.
Here, .DELTA.- is another design parameter. If the current queue
length lies between the upper threshold and the lower threshold
because there is little difference between the current queue length
and the reference length, the bandwidth change is not
requested.
[0038] Alternatively, the change in bandwidth can be requested in
relation to the error or difference between the current queue
length and the target queue length as shown in FIG. 4B. When the
current queue length is greater than the reference length, for
example when packets are stored in the queue because of
insufficient bandwidth allocated to the subscriber station,
additional bandwidth can be requested in proportion to the
difference between the current queue length and the reference
length. Similarly, when the current queue length is less than the
reference length because of excessive bandwidth allocated to the
subscriber station, a decrease of the bandwidth can be requested in
proportion to the difference. Compared to FIG. 4A, the current
queue length can be converged rapidly to the target length when
there is a large discrepancy between the current queue length and
reference length. It is also to be understood that, although FIG.
4B illustrates a linear relationship having slope K between a
change in the bandwidth-request and the difference between the
reference and current queue length, this is merely for example.
That is, the relationship may be altered as well as being replaced
by a non-linear function.
[0039] As shown in FIG. 4C, the bandwidth-request can also be
determined by combining the methods of FIGS. 4A and 4B. As
illustrated in FIG. 4C, the bandwidth request may be computed in
proportion to the queue length error as discussed with reference to
FIG. 4B. Also, when there is little difference between the current
queue length and the target length, that is when the current queue
length lies between the upper threshold and the lower threshold, no
bandwidth change can be requested as discussed with reference to
FIG. 4A. Thus, the current queue length can be converged rapidly to
the target length while unnecessarily frequent bandwidth requests
can be avoided.
[0040] However, using merely the queue length control, it is
difficult to converge the current queue length rapidly to the
reference length in response to the fast variation of the packet
arrival rate. Therefore, exemplary embodiments of the present
invention determine the amount of bandwidth-request through the
additional control based on the change rate of queue length. More
specifically, the bandwidth requesting apparatus determines the
bandwidth-request amount y.sub.r(t) using the estimated change rate
of queue length e.sub.r(t) in step 205.
[0041] The bandwidth-request amount can be computed in proportion
to the change rate of queue length e.sub.r(t), which is expressed
as Equation (1).
y.sub.r(t)=g(e.sub.r(t)) (1)
[0042] The function g( ) can vary similar to that shown in FIGS. 4A
to 4C. The change rate of queue length can be expressed as Equation
(2).
e r ( t ) = a ( t ) - s ( t ) = t q ( t ) = t e q ( t ) ( 2 )
##EQU00001##
[0043] In Equation (2), a(t) indicates the queue input rate, that
is, the packet arrival rate. Also in Equation (2), s(t) indicates
the service rate from the bandwidth allocating apparatus and
e.sub.q(t) indicates the queue length error. That is, e.sub.q(t)
indicates the difference between the actual queue length q(t) and
the reference length q.sub.ref.
[0044] In step 207, the bandwidth requesting apparatus computes the
final bandwidth-request amount B(t) by adding the calculated
bandwidth-request amounts y.sub.q(t) and y.sub.r(t).
[0045] The amount of the final additional bandwidth-request can be
expressed as Equation (3).
B(t)=y.sub.q(t)+y.sub.r(t) (3)
[0046] In step 209, the bandwidth requesting apparatus sends
information of the calculated final bandwidth-request amount to the
bandwidth allocating apparatus. The final bandwidth-request amount
information can be transmitted by piggybacking on UL packets. In
the piggyback transmission, the bandwidth requesting apparatus can
send the information of the calculated final bandwidth-request
amount using an Extended Piggyback Bandwidth Request (EPBR) field
of a grant management subheader of a Media Access Control (MAC)
header.
[0047] Next, the bandwidth requesting apparatus finishes this
process.
[0048] The exemplary UL bandwidth requesting algorithm of the
present invention can be expressed as a general
Proportional-Derivative (PD) controller for the queue length error
e.sub.q(t) as in Equation (4). While the proportion control is
based on the current queue length error, the derivative control is
based on the change rate of queue length. The system is stabilized
by promptly responding to the queue length change.
B ( t ) = f ( e q ( t ) ) + g ( t e q ( t ) ) ( 4 )
##EQU00002##
[0049] To implement the continuous-time controller of Equation (4)
as a discrete-time controller, the derivative term can be
approximated as in Equation (5).
t e q ( t ) = e q [ n ] - e q [ n - 1 ] T a ( 5 ) ##EQU00003##
[0050] In Equation (5), T.sub.a indicates a bandwidth allocation
period. When the exemplary UL bandwidth requesting algorithm of the
present invention is expressed as the general PD controller for the
queue length error e.sub.q(t), the algorithm can be realized using
only the information of the current queue length and the previous
queue length.
[0051] FIG. 3 is a flowchart illustrating a method of allocating a
UL bandwidth according to an exemplary embodiment of the present
invention.
[0052] In step 301, the bandwidth allocating apparatus determines
whether the additional bandwidth-request amount information is
received from the bandwidth requesting apparatus.
[0053] When receiving the additional bandwidth-request amount
information, the bandwidth allocating apparatus assigns the
previously allocated bandwidth and the bandwidth as additionally
requested, to the bandwidth requesting apparatus through scheduling
in step 303 and receives UL data from the bandwidth requesting
apparatus over the allocated bandwidth in step 305.
[0054] Next, the bandwidth allocating apparatus finishes this
process.
[0055] FIG. 5 is a graph for comparing a queue length variation
between a conventional algorithm and an exemplary algorithm of the
present invention. In experiments for the algorithm comparison, the
input traffic is generated such that a packet is generated every 20
ms and its size is determined according to an exponential
distribution with an average value of 500 bytes. With the MAC
overhead considered, the average data rate of the input traffic is
about 225 kbps.
[0056] According to the conventional UGS algorithm in FIG. 5, the
queue length is repeatedly increased and decreased based on the
packet input rate variation. This may result in an increase of
jitter. In the conventional rtPS algorithm, the queue length is
unstable because of the time delay between packet arrival and
bandwidth allocation by responding to the poll, during which the
queue length may continue to increase up to the maximum buffer
capacity. If the time delay is excessive and the number of packets
received is greater than the maximum buffer capacity, packets may
be lost. By contrast, in the exemplary ertPS algorithm of the
present invention, the queue length is kept close to the reference
value of 10 packets, as illustrated in FIG. 5. The exemplary ertPS
algorithm of the present invention can regulate the queue length
through the feedback based on the change rate of queue length.
[0057] FIG. 6 is a graph for comparing a packet arrival rate and a
queue service rate according to an exemplary algorithm of the
present invention.
[0058] The queue service rate according to the resource allocation
follows the arrival rate of the input packet well. Hence, as
illustrated in FIG. 6, there is little difference in the two
rates.
[0059] The exemplary ertPS algorithm of the present invention meets
the desired QoS with the minimum resources. To prove this, when the
average arrival rate of the packets is 225 kbps in consideration of
the MAC overhead and minimum reserved rates are 200 kbps, 225 kbps
and 250 kbps, the packet loss rate, the bandwidth waste rate, the
average delay, and the jitter (calculated as the standard deviation
of the delay) of the UGS, the rtPS, and the ertPS are compared as
below.
[0060] Table 1 compares the performance in a well-provisioned case
where the minimum reserved rate is 225 kbps, Table 2 compares the
performance in an under-provisioned case where the minimum reserved
rate is 200 kbps, and Table 3 compares the performance in an
over-provisioned case where the minimum reserved rate is 250
kbps.
TABLE-US-00001 TABLE 1 Algorithms UGS rtPS ertPS Packet loss rate
(%) 0 2.17 0 Bandwidth waste (%) 7.17 1.20 0.37 Delay (ms) 150.9
1843.6 212.7 Jitter (ms) 137.5 703.9 61.8
TABLE-US-00002 TABLE 2 Algorithms UGS rtPS ertPS Packet loss rate
(%) 5.76 4.07 0 Bandwidth waste (%) 0.30 1.19 0.52 Delay (ms)
2002.5 1825.6 212.9 Jitter (ms) 770.0 681.5 64.8
TABLE-US-00003 TABLE 3 Algorithms UGS rtPS ertPS Packet loss rate
(%) 0 2.54 0 Bandwidth waste (%) 15.38 1.20 0.45 Delay (ms) 85.8
1859.5 206.9 Jitter (ms) 73.0 670.5 60.9
[0061] In the under-provisioned case, the time delay drastically
increases (greater than 13 times as compared to the
well-provisioned case) and the packet loss rate is close to 6%,
because the conventional UGS assigns a fixed-sized bandwidth. In
the over-provisioned case, the packet loss and the time delay
decrease, whereas the bandwidth waste rate reaches 15%. The
conventional rtPS results in the considerable time delay and jitter
regardless of the minimum reserved rate, and the packet loss rate
is about several percentages. This is because the conventional rtPS
cannot assign the bandwidth timely due to the polling delay when
the bandwidth is requested based on the current queue length. By
contrast, the ertPS according to exemplary embodiments of the
present invention keeps the bandwidth waste below 0.5%, suffers no
packet loss, and controls the time delay in the proximity of the
target value (200 ms), regardless of the bandwidth provisioning
level. Also, the jitter is minimized compared to the other
algorithms.
[0062] As set forth above, an exemplary broadband wireless access
system of the present invention adopts a target or reference value
of the queue length, calculates a UL bandwidth-request amount in
proportion to the difference between the current queue length and
the target length, calculates a UL bandwidth-request amount in
proportion to not only the queue length but the change rate of
queue length, and then determines the amount of the final
bandwidth-request using these two terms. Therefore, the queue
length can be quickly converged to the target value. Exemplary
methods of the present invention can reduce the jitter due to the
queuing delay and control the queuing delay by setting the target
length. Even when characteristics of the input traffic or the radio
channel rapidly vary, the exemplary method requests the bandwidth
by quickly and accurately predicting the amount of required
bandwidth. Thus, with the minimum bandwidth, the QoS can be
guaranteed, the unnecessary bandwidth waste can be minimized, and
the radio resources can be utilized efficiently. Further, exemplary
embodiments of the present invention are flexibly applicable based
on the condition of the application or the system. For instance, in
a rapidly changing system, a greater weight is applied to the term
which is proportional to the change rate of queue length. To
regulate the time delay at an intended level or to minimize the
jitter, a greater weight can be applied to the term which is
proportional to the queue length.
[0063] While the invention has been shown and described with
reference to certain exemplary embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims and
their equivalents.
* * * * *